For example, Japanese Laid-Open Patent Publication No. 9-262120 discloses a conventional ultrasonic hair treatment device having a vibration element for converting electric signals to mechanical vibrations in an ultrasonic range, in which ultrasonic vibrations generated by the vibration element are applied to hairs and hair treatment agent so as to accelerate impregnation of the hair treatment agent into the hairs.
The ultrasonic hair treatment device comprises a pair of pinching members which are rotatable coupled with each other at an end of each pinching members, a vibrator having a disc shaped vibration element and provided at a free end of one pinching member and a receiver provided at a free end of the other pinching member so as to face the vibrator. For example, a bundle of hairs to which the hair treatment agent is spread is pinched between flat faces of the vibrator and the receiver. Under such a condition, the ultrasonic hair treatment device is moved along lengthwise direction of the bundle of hairs (or a direction for extending the hairs), while applying the ultrasonic vibrations generated in thickness direction by the vibration element to the hairs and the hair treatment agent. Thereby, impregnation of the hair treatment agent into the hairs entirely along the lengthwise direction can be accelerated.
Since the vibration element of the conventional ultrasonic hair treatment device is a disc shape, amplitude of the vibrations in the thickness direction becomes the largest at the center portion of the disc shape, and the amplitude of the vibration becomes smaller as departing from the center toward periphery in radial direction of the disc shape. In other words, resonance point, that is, the point where the amplitude of vibrations in the thickness direction becomes the largest of the disc shaped vibration element is only positioned at the center of the disc shape, so that the vibration element rarely vibrates the hairs and the hair treatment agent at the peripheral portion thereof, although it can vibrate the hairs and the hair treatment agent sufficiently at the center portion. Consequently, it is difficult to impregnate the hair treatment agent into the hairs entirely even in widthwise direction of the bundle of hairs.
Furthermore, since the hair treatment agent cannot be impregnated into the hairs sufficiently at the periphery portion of the disc shape of the vibration element, especially, at both end portion of the bundle of hairs in the widthwise direction thereof perpendicular to the longitudinal direction of the bundle of hairs, a treatment time necessary for treating the hairs becomes longer. Still furthermore, since the hairs are pinched between the flat faces of the vibrator and the receiver, the hair treatment agent cannot contact with the hairs completely, and thus, the hair treatment agent cannot be impregnated into the hairs sufficiently. Still furthermore, the hairs at a position corresponding to the resonance point of the vibration element may not be spread the hair treatment agent sufficiently while the hairs are pinched between the vibrator and the receiver, so that the hair treatment agent cannot be impregnated into the hairs effectively.